Method and apparatus for imaging of vessel segments

ABSTRACT

An apparatus, method and software arrangement for imaging a surface of a structure that is in contact with an opaque fluid is provided. The apparatus includes an article of manufacture (e.g., a housing), a fluid delivery arrangement and an imaging arrangement. The housing includes an aperture formed in the article of manufacture. The fluid delivery arrangement is configured to deliver a volume of substantially transparent fluid to the aperture formed in the housing. The imaging arrangement is configured to image the surface of the structure using an imaging modality after the volume of the transparent fluid is delivered to the aperture, wherein the imaging arrangement and/or the article of manufacture is translated along the surface of the structure while imaging the surface of the structure.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of, and therefore claimspriority from U.S. application Ser. No. 11/211,483, filed on Aug. 24,2005, now U.S. Pat. No. 8,208,995 issued on Jun. 26, 2012 which claimspriority from U.S. Patent Application Ser. No. 60/604,138 filed on Aug.24, 2004. The entire disclosures of both applications are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus that use opticalradiation for imaging surfaces and, more particularly to a method andapparatus that use optical radiation to image an interior target surfaceof a blood vessel.

BACKGROUND INFORMATION

Acute myocardial infarction (“AMI”) is the leading cause of death in theUnited States and industrialized countries. Research conducted for overthe past 15 years has demonstrated that several types of minimally ormodestly stenotic atherosclerotic plaques, termed vulnerable plaques,are precursors to coronary thrombosis, myocardial ischemia, and suddencardiac death. Postmortem studies have identified one type of vulnerableplaque, i.e., the thin-cap fibroatheroma (“TCFA”), as the culprit lesionin approximately 80% of sudden cardiac deaths. Over 90% of TCFA's arefound within the most proximal 5.0 cm segment of each of the maincoronary arteries (left anterior descending—LAD; left circumflex—LCx;and right coronary artery—RCA). The TCFA is typically a minimallyocclusive plaque characterized histologically by the following features:a) thin fibrous cap (<65 μm) large lipid pool, and c) activatedmacrophages near the fibrous cap. It is hypothesized that these featurespredispose TCFAs to rupture in response to biomechanical stresses.Following the rupture, the release of procoagulant factors, such astissue factor, create a nidus for thrombus formation and the potentialfor an acute coronary event. While TCFAs are associated with themajority of AMIs, recent autopsy studies have shown that coronaryplaques with erosions or superficial calcified nodules may alsoprecipitate thrombosis and sudden occlusion of a coronary artery.

Although autopsy studies have been valuable in determining features ofculprit plaques, the retrospective nature of these studies may limittheir ability to quantify the risk of an individual plaque for causingacute coronary thrombosis. For instance, TCFAs are a frequent autopsyfinding in asymptomatic or stable patients, and are found with equalfrequency in culprit and non-culprit arteries in acute coronarysyndromes. Moreover, disrupted TCFAs have been found in about 10% ofnon-cardiac deaths. Recent findings of multiple ruptured plaques andincreased systemic inflammation in acute patients have challenged thenotion of a single vulnerable plaque as the precursor for AMI. A betterunderstanding of the natural history and clinical significance of theselesions may accelerate progress in the diagnosis, treatment andprevention of coronary artery disease.

An exemplary approach to studying the evolution of vulnerable plaques isa non-invasive or intracoronary imaging of individual lesions atmultiple points in time. Unfortunately, the microscopic features thatcharacterize vulnerable plaque are not reliably identified by theconventional imaging technologies, such as intravascular ultrasound(“IVUS”), catscan (“CT”), and magnetic resonance imaging (“MRI”). Whileexperimental intracoronary imaging modalities such integratedbackscatter IVUS, elastography, angioscopy, near-infrared spectroscopy,Raman spectroscopy and thermography have been investigated for thedetection of vulnerable plaque, it is believed that no method other thanoptical coherence tomography (“OCT”) has been shown to reliably identifythe characteristic features of these lesions.

OCT is an optical analog of ultrasound that provides high-resolution(˜10 μm) cross-sectional images of human tissue. OCT has beenestablished as an accurate method for characterizing the microscopicfeatures associated with vulnerable plaque. This technology can also beused to quantify macrophage content within atherosclerotic plaque.Intracoronary optical imaging using such technology is safe, and imagesobtained from patients have features substantially identical to thoseidentified ex vivo. Thus, OCT has the ability to provide a large amountof information about plaque microstructure. This technology may play animportant role in improving the understanding of vulnerable coronaryplaques in patients.

Strong attenuation of light in blood may present a significant challengefor intravascular optical imaging methods. To overcome this potentialobstacle, intermittent 10 cc flushes of saline through a guidingcatheter can provide an average of 2 seconds of clear viewing duringwhich effective images can be captured, as is shown in FIG. 1B. Forexample, FIG. 1B illustrates an analysis of the time of angiographiclumen attenuation following a 6 cc contrast injection at three separatelocations, shown in part A of FIG. 1B. As can be seen from part B ofFIG. 1B, the angiographic lumen attenuation following the 6 cc contrastinjection at a rate of 3 cc/s demonstrates a complete filling for theduration of the purge (approximately 2 seconds) regardless of thelocation. Additionally, saline flushing of a blood vessel for a limitedduration (for example, less than 30 seconds) is safe, and generally doesnot result in a myocardial ischemia. This approach can provideexceptional cross-sectional images of coronary vasculature. However, thecombination of the limited flush duration and low image acquisition ratemay reduce comprehensive coronary screening.

One proposed solution has been to change the optical properties ofblood. The primary mechanism of optical attenuation in blood is opticalscattering. For instance, matching the refractive index of the red bloodcells, white blood cells and platelets with that of a serum decreasesoptical scattering. This approach has resulted in a 1.5-fold increase inpenetration of OCT when diluting blood with Dextran. Unfortunately,since the optical attenuation of blood is so high, at least a 10-foldimprovement would be preferable to allow for effective intracoronary OCTimaging in patients.

Another proposed solution is to completely occlude the artery, andreplace blood with saline. This technique that is commonly deployed inangioscopic imaging requires proximal balloon occlusion. Followingvascular occlusion, all of the remaining blood in the vessel is replacedwith saline. This conventional method allows a cross-sectional opticalimaging of the entire coronary tree. While this procedure is commonlyconducted in Japan, the potential for coronary dissection and myocardialischemia precludes widespread clinical application of this procedure.

Still another proposed solution is to purge the blood vessel withoptically transparent blood substitutes. Blood substitutes that aretransparent in the infrared can potentially provide clear imaging for anextended duration. This method has achieved significantly improvedimaging in murine myocardium by replacing blood with Oxyglobin. Althoughthese compounds may hold promise for future clinical application, theyare not yet approved for human use.

A further proposed solution is to increase the frame rate of OCT scans.Since the goal is to acquire a sufficient number of images tocomprehensively screen coronary arteries, a straightforward approachwould be to accept the clear viewing time provided by conventionalsaline flushing, and increase the frame rate of OCT scans dramatically.Two possibilities exist for increasing the frame rate of OCT scans: areduction of the number of A-lines per image, and an increase of theradial scan rate.

Similarly to many imaging methods, OCT images are acquired in a pointsampling fashion and are composed of multiple radial scans or A-lines.To increase the image rate, it is possible to reduce the number ofA-lines per image by increasing the catheter rotation rate. Imagequality degrades rapidly in such case, however, manifested by a decreasein transverse resolution as can be seen in FIG. 1A. For example, image Aof FIG. 1A depicts a sample image generated using OCT imaging at a rateof 4 frames per second having 500 A-line scans per frame. Image B ofFIG. 1A depicts a sample image generated using OCT imaging at a rate of40 frames per second having 50 A-line scans per frame. As can be clearlyseen, the image quality of Image A far exceeds the image quality ofImage B. This degradation is unacceptable for most clinicalapplications.

A second possibility is to increase the radial scan rate. For technicalreasons specific to the current OCT paradigm, an increase in A-line ratemay result in an unacceptable penalty in signal to noise ratio, andthus, images of sufficient quality for accurate diagnosis cannot beobtained.

Therefore, there is a need to provide a method and apparatus thatcombine quality imaging of internal surfaces of blood vessels and otherbiological structures and effective imaging of segments of the internalsurfaces of the blood vessels.

SUMMARY OF THE INVENTION

It is therefore one of the objects of the present invention to providean apparatus and method that combine quality imaging of internalsurfaces of blood vessels and other biological structures and effectiveimaging of segments of the internal surfaces of the blood vessels.Another object of the present invention is to provide an apparatus andmethod that provide quality images of internal surfaces of segments ofblood vessels in order to offer an improved understanding of the naturalhistory and clinical significance of these lesions which will accelerateprogress in diagnosis, treatment and prevention of coronary arterydisease.

These and other objects can be achieved with the exemplary embodiment ofthe apparatus, method and software arrangement according to the presentinvention for imaging a structure that is in contact with an opaquefluid. The exemplary apparatus can include a housing, a fluid deliveryarrangement and an imaging arrangement. The fluid delivery arrangementis configured to deliver a volume of further fluid to an externallocation with respect to the housing. And the imaging arrangement isconfigured to image the structure after the volume of the further fluidis delivered to the external location, wherein the imaging arrangementis translated along a path which approximately corresponds to an axis ofextension of a surface while imaging the structure.

In another exemplary embodiment of the apparatus, method and softwarearrangement according to the present invention for imaging a structurethat is in contact with an opaque fluid. The exemplary method includesinjecting a bolus of transparent or semi-transparent fluid into thevessel, imaging the vessel using rapid circumferential and pull-backimaging to achieve a helical or three-dimensional scan, evaluating imagequality during the pull-back, discontinuing imaging when image qualityfalls below a given level, and taking steps to improve image quality,including repeating the above procedure.

According to another exemplary embodiment of the present invention,apparatus, method and software arrangement are provided for imaging astructure (e.g., a blood vessel) that is in contact with a first fluid.A volume of a second fluid is delivered by a fluid delivery arrangementconfigured to an external location with respect to, e.g., an article ofmanufacture (e.g., a housing). The structure can be imaged. e.g., usingan imaging arrangement during or after the volume of the second fluid(e.g., a transparent fluid) is delivered to the external location. Forexample, the imaging arrangement or the article of manufacture can betranslated along a path which approximately corresponds to an axis ofextension of a surface while imaging the structure. The fluid deliveryarrangement can be a pump or syringe that is operatively connected tothe article of manufacture. a syringe operatively connected to thearticle of manufacture.

The article of manufacture can include an aperture formed in the articleof manufacture. The fluid delivery arrangement may include a transparentfluid reservoir containing the second fluid, and a delivery conduithaving a first end connected to the second fluid reservoir and a secondend connected to the aperture of the article of manufacture. Theaperture of the housing can be located at a distal end of the housing oradjacent to the imaging arrangement. The imaging arrangement may includea directing arrangement configured to direct light to a surface of thestructure, at least one optical fiber operatively connected to thedirecting arrangement, and an image processing arrangement operativelyconnected to the at least one optical fiber. The directing arrangementcan include optics at the distal end of the imaging arrangement, and/ora lens and a light directing element. Further, the directing element canbe an optical arrangement which is configured to alter at least onedirection of light, and the optical arrangement is capable of directingthe light from a direction substantially parallel to the greater axis ofthe housing to a direction substantially perpendicular to the greateraxis of the article of manufacture. The lens can focus the lightapproximately 0.5 mm to 5 mm beyond the article of manufacture.

A rotating arrangement can be provided that is operatively connected tothe imaging arrangement, and configured to rotate the imagingarrangement. The rotating arrangement may rotate at a rate of at leastabove approximately 30 rotations/second and at most approximately 1000rotations/second. The imaging arrangement may be rotated within thearticle of manufacture while imaging the structure. A pull-backarrangement can be provided that is operatively connected to the imagingarrangement, and configured to translate the imaging arrangementrelative to the article of manufacture. The pull-back arrangement maytranslate the imaging arrangement at a rate of at least approximately 1mm/second and at most approximately 100 mm/second, and/or at a rate ofapproximately 10 mm/second.

At least a portion of the article of manufacture can be transparent. Theimaging modality may be time domain optical coherence tomography, aspectral domain optical coherence tomography or a optical frequencydomain imaging. The second fluid can be substantially transparent toradiation utilized by the imaging modality. A guide catheter configuredto receive the article of manufacture therein can be provided. The fluiddelivery arrangement can deliver the fluid to a proximal end of theguide catheter, and the fluid may flow through an aperture formedthrough the guide catheter.

The imaging arrangement can obtain data associated with the structure,and a processing arrangement may provided to receive the data, andcapable of controlling at least one of the fluid delivery arrangementand the imaging arrangement as a function of the data. The processingarrangement may control the fluid delivery arrangement or the imagingarrangement based on information previously received by the processingarrangement. The processing arrangement may also control the translationof the imaging arrangement, the fluid delivery of the fluid deliveryarrangement, and/or the translation of the imaging arrangement and thefluid delivery of the fluid delivery arrangement. A catheter can beprovided which includes the article of manufacture or the imagingarrangement. The fluid delivery arrangement may deliver the second fluidthrough an internal portion of the catheter. The imaging arrangement mayinclude imaging optics which emit a beam to obtain the image, the beambeing transmitted outside of the catheter.

These and other objects, features and advantages of the presentinvention will become apparent upon reading the following detaileddescription of embodiments of the invention, when taken in conjunctionwith the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is now made to the following description, taken inconjunction with the accompanying drawings, in which:

FIG. 1A shows images of the interior surface of a blood vessel gatheredusing OCT imaging at different settings;

FIG. 1B illustrates an analysis of the time of angiographic lumenattenuation following a contrast injection at three separate locationsin a given blood vessel;

FIGS. 2A-2B show an exemplary embodiment of an imaging catheter forconducting scans of a segment of a blood vessel;

FIG. 3 shows an exemplary embodiment of a flow chart depicting a processfor gathering information representative of a helical scan of a segmentof a blood vessel using the imaging catheter of FIGS. 2A-2B;

FIG. 4 shows the imaging catheter of FIG. 2A after retraction of arotateable inner shaft of the imaging catheter;

FIG. 5 illustrates an exemplary embodiment of an enlarged section of theimaging catheter of FIG. 2A as defined by the dashed box A; and

FIG. 6 shows the imaging catheter of FIG. 2A, enclosed within a guidecatheter, whereby a transparent solution is injected into the guidecatheter enclosing the imaging catheter.

Throughout the drawings, the same reference numerals and characters,unless otherwise stated, are used to denote like features, elements,components, or portions of the illustrated embodiments. Moreover, whilethe present invention will now be described in detail with reference tothe Figures, it is done so in connection with the illustrativeembodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 2A, 2B, 4, 5 and 6 illustrate various exemplary embodiments of anapparatus for obtaining an image of internal surfaces of a segment of ananatomic structure and FIG. 3 shows an exemplary embodiment of a methodto implant the same. Generally, the exemplary method and apparatusaccording to the present invention perform a helical scan of theinternal surfaces of the segment of the anatomic structure afterinjecting a bolus of transparent or semi-transparent fluid, so as toobtain an image of the internal surfaces of the segment of the anatomicstructure using an imaging modality. Such technique combines theefficacy of the imaging modality and the process of injecting a bolus oftransparent or semi-transparent fluid with the beneficial effect ofimaging an entire segment of the anatomic structure. The exemplaryembodiments of the method and apparatus according to the presentinvention utilize a further paradigm for imaging that provide asignificant increase in the image acquisition rate, while preserving agood image quality. According to one exemplary embodiment, the dramaticincrease represents at least an approximately 10-fold increase in theimage acquisition rate. With this exemplary technology, comprehensivecoronary imaging can be achieved using conventional methods oftransparent or semi-transparent fluid flushing in conjunction withautomatic catheter pullback. In one exemplary embodiment of the presentinvention, this new paradigm utilizes Optical Frequency Domain Imaging(“OFDI”) as an imaging modality to obtain these images. In anotherexemplary embodiment, the anatomic structure can be a blood vessel.

It should be understood that alternate imaging modalities that detectsingle scattered light, such as time domain OCT and confocal microscopy,can also be used.

In a further exemplary embodiment of the present invention (as shown inFIG. 2A), the imaging module 224 utilizes OCT, visible light imaging,spectroscopy and/or thermoography. In another exemplary embodiment, theOCT imaging modality used is time-domain OCT (“TD-OCT”), spectral-domainOCT (“SD-OCT”), optical frequency domain imaging (“OFDI”), and/orlow-coherence interferometry. In still another exemplary embodiment ofthe present invention, the visible light imaging modality used isintracoronary angioscopy, speckle imaging, fluorescence imaging, and/ormulti-photon imaging. In yet another exemplary embodiment of the presentinvention, the spectroscopy modality uses visible light having aspectrum of approximately 0.3-0.7 μm, near infrared light (“NIR”) havinga spectrum of approximately 0.7-2.2 μm, infrared light (“IR”) having aspectrum of approximately 2.2-12 μm, Raman scattered light and/orfluorescent light. In a further exemplary embodiment of the presentinvention, the imaging module 224 utilizes ultrasound, particularlyhigh-frequency ultrasound having a frequency of at least approximately20 MHz. In a still further exemplary embodiment of the presentinvention, the imaging assembly 204 includes a lens, mirror and/orprism.

FIGS. 2A and 2B illustrate an exemplary embodiment of an imaging system200 including a specially modified optical catheter 202 having a distalend 220 and a proximal end 222. The imaging system 200 is capable ofimaging long arterial segments by utilizing a rapid acquisition rate ofimaging modalities and implementing automated pullback of the imagingcatheter 202. These efforts may allow a proximal portion of each maincoronary artery (LAD, LCx, and RCA) to be comprehensively imaged with aspecific longitudinal image spacing, while administering a safe totalamount of transparent or semi-transparent fluid to the patient.

In one exemplary embodiment of the present invention, long arterialportion that is up to 10 cm in length can be examined. In anotherexemplary embodiment, the long arterial portion of up to 5.0 cm inlength can be examined. In still another exemplary embodiment, theproximal portion of each main coronary artery is up to 10 cm in lengthwhich is capable of being examined. In still another exemplaryembodiment of the present invention, the proximal portion of each maincoronary artery is up to 5 cm in length which is capable of beingexamined. In still another exemplary embodiment of the presentinvention, the specific longitudinal imaging spacing is betweenapproximately 100 μm and approximately 150 μm, preferably approximately125 μm. In still another exemplary embodiment of the present invention,the specific longitudinal imaging spacing matches the transverse spotdiameter, and is therefore between approximately 15 μm and approximately35 μm, preferably approximately 25 μm. In yet another exemplaryembodiment of the present invention, the safe total amount oftransparent or semi-transparent fluid is at most 150 cc/artery, andpreferably no more than 30 cc/artery. In another exemplary embodiment ofthe present invention, the transparent or semi-transparent fluid can benormal saline, ½ normal saline, ¼ normal saline, lactated ringerssolution, phosphate buffered saline, blood substitute such as Oxyglobin,and/or coronary contrast media. In a further exemplary embodiment of thepresent invention, the imaging system 200 may image segments of anyblood vessel including: carotid arteries, iliac arteries, femoralarteries, popliteal arteries, radial arteries, other peripheral arteriesand veins.

Blood presents a challenge for any light-based intravascular imagingmodality. As light propagates in blood, certain information is lost dueto both scattering and absorption. At a wavelength of approximately 1.3μm, the combined attenuation due to scattering and absorption can beminimized Even at this optimal wavelength, however, imaging vascularstructure through blood may not be feasible. Particular preferences forimaging may include a high signal-to-noise ratio (“SNR”) and a highimage quality requiring substantial amounts of detail. If OCT imaging isutilized as the imaging modality, a large number of A-lines arepreferable in each OCT scan. Clear OCT imaging may be achieved for shortdurations, e.g., on the order of three (3) seconds, by temporarilydisplacing blood using a bolus injection of transparent orsemi-transparent fluid through the catheter 200. Therefore, at animaging rate of four (4) frames per second, a single transparent orsemi-transparent fluid purge may provide approximately 12 high-qualityOCT images before blood reenters the field of view.

In a further exemplary embodiment of the present invention, the bolusinjection of transparent or semi-transparent fluid can introduceapproximately between 1 and 50 cc of transparent or semi-transparentfluid into the blood vessel. In another exemplary embodiment of thepresent invention, the bolus injection of transparent orsemi-transparent fluid introduces approximately 10 cc of transparent orsemi-transparent fluid into the blood vessel.

According to these embodiments, a modified optical catheter 200, probeor other instrument may be inserted into a blood vessel (e.g., artery)to image the vessel. When plaque is located, the probe is moved into theproximity of the specific atherosclerotic plaque. Light reflected fromthe interior wall of the blood vessels and/or from a plaque is collectedand transmitted to a detector 236 of an imaging module 224.

In an exemplary embodiment of the present invention, pathologies otherthan plaque may be imaged, for example, thrombus, dissections, rupture,stents, and the like.

Referring to FIG. 2A, the specially modified optical catheter 202 mayinclude a rotatable inner shaft 210 and an outer sheath 208. Therotatable inner shaft 210 houses a fiber array 218 and an imagingassembly 204 near the distal end 220 of the catheter 202. The outersheath 208 includes an aperture 221 formed therethrough. The aperture221 is connected to a fluid delivery channel 223, which is in turnconnected to a fluid pump 225. The fluid pump 225 can cause theinjection of a specific volume of transparent or semi-transparent fluidthrough the fluid delivery channel 223 and out from the aperture 221,thereby displacing the liquid surrounding the distal end 220 of thecatheter 202 with the injected bolus. The fiber array 218 of thecatheter 202 connects to a rotary junction 212, which is in turnconnected to a fixed optical fiber 214 that it extends from the catheter202 proximally to the imaging module 224. The rotary junction 212 isalso connected to a pullback device 215. The pullback device 215translates the rotatable inner shaft 210 within the outer sheath 208when instructed by a processor 240 during imaging, such that a helicalscan can be generated. FIG. 4 illustrates the catheter 202 afterpullback of the rotatable inner shaft 210 has been completed, otherwisethe system 200 of FIG. 4 is identical to the system 200 of FIG. 2A. Theprocess 300 by which the imaging system 200 gathers data representativeof a helical scan of a section of the blood vessel is illustrated inFIG. 3, and described in more detail herein.

In an exemplary embodiment of the present invention, the outer sheath208 of the catheter 202 is not transparent. For example, during thepull-back the entire catheter 202, the outer sheath 208 is translatedthrough the blood vessel, while the internal shaft 210 rotates. In thisexemplary embodiment, the internal shaft 210 is not translated relativeto the outer sheath 208. In another exemplary embodiment, the fiberarray 218 includes a single fiber. In still another exemplaryembodiment, the fiber array 218 includes a number of fibers.

The catheter 202 can be fabricated using an FDA approved 2.6-3.2F IVUScatheter. The inner core of the IVUS catheter is capable of rotating andobtaining cross-sectional images at, e.g., 40 frames per second. Theultrasound transducer and conductive wire, which are generally used inthe IVUS catheter, may be removed and replaced with the imaging assembly204, the fiber array 218, the inner shaft 210, the fluid deliverychannel 223 and an aperture is formed through the aperture of the outersheath of the IVUS catheter. The newly provided inner shaft 210 of theIVUS catheter rotates to provide circumferential scanning and may bepulled back for screening a segment of a blood vessel. The transparentouter sheath 208, which incorporates a monorail guide wire (not shown),does not rotate and is plugged at the distal end of the IVUS catheterusing an FDA approved polymer. The catheter 202 is also attached to therotary junction 212.

In an exemplary embodiment, the catheter 202 includes a rotating opticalfiber within a flexible inner cable. The flexible inner cable iscontained within an outer transparent housing or sheath. The outerhousing may include a monorail guide wire. The rotating optical fiberand the flexible inner cable each have a distal end and a proximal end.The rotating optical fiber and the flexible inner cable are orientedsuch that the distal end of the rotating optical fiber and the distalend of the flexible inner cable are adjacent to one another, and theproximal end of the rotating optical fiber and the proximal end of theflexible inner cable are adjacent to one another. Distal opticsincluding a lens and a beam directing element are attached to the distalend of the flexible inner cable. An optical rotating junction isprovided at the proximal end of the rotating optical fiber. The rotatingoptical fiber couples a static optical fiber to the rotating opticalfiber within the flexible inner cable. The optical rotating junctionrotates the rotating optical fiber, the flexible inner cable and thedistal optics to provide circumferential optical sampling of the luminalsurface of the vessel. The optical fiber, inner flexible cable, anddistal optics rotate and an image is obtained for each catheterrotation. The inner optical cable is pulled back longitudinally withinthe outer transparent housing to form a helical scan of the vessel.

In an exemplary embodiment, the beam directing element is a prism thatdirects the beam substantially perpendicular to the catheter axis andthe lens focuses the beam to approximately 2 mm from the outer sheath.In another exemplary embodiment, the rotation rate ranges fromapproximately 10 per second to approximately 100 per second andpreferably approximately 30 per second. In still another embodiment, theentire catheter including the transparent outer sheath is pulled backwithin the lumen of the vessel. In a further preferred embodiment, thepull back rate ranges from approximately 1 mm/second to approximately 20mm/second and preferably approximately 10 mm/second.

In an exemplary embodiment, the monorail guide wire is similar to theguide wire as described in U.S. Pat. No. 5,350,395, entitled“Angioplasty Apparatus Facilitating Rapid Exchanges,” to Paul G. Yock,issued Sep. 27, 1994, and incorporated herein in its entirety.

The entire shaft 210 of the catheter 202 can rotate 360 degrees,allowing the catheter 202 to gather images of the subject tissue 250around the entire circumference of the catheter 202. In one exemplaryembodiment of the present invention, the catheter 202 can obtain imagesof a plaque around the circumference of an interior vessel wall.

In operation, a coherent light, such as laser light, is transmitted froma light source 232 via beam-splitter 234, through the fixed opticalfiber 214 and central fiber 226 and onto the imaging assembly 204. Thelight is directed via the imaging assembly 204 to a subject tissue 250(arrow 206). According to an exemplary embodiment of the presentinvention, the subject tissue 250 may be a layer of static tissue over alayer of moving tissue, such as an atherosclerotic plaque. The outersheath 208 can be placed directly in contact with the sample 250 and/orcan be positioned at a short distance (e.g., 1 mm to 10 cm) away fromthe sample. For example, light can enter sample 250, where it isreflected by molecules, cellular debris, proteins, compounds (e.g.,cholesterol crystals), and cellular microstructures (such as organelles,microtubules) within the subject tissue 250. Light remitted from thesubject tissue 250 (shown by arrows 228 in FIG. 2B, the remainder ofFIG. 2B is identical to FIG. 2A) is conveyed through the imagingassembly 204 to the single optical fiber or fibers of the fiber array218, and then transmitted by the optical fiber or fiber array 218 to thedetection device 236, via the beam-splitter 234. In another embodiment,the device transmitting light to the catheter and receiving light fromthe catheter is an optical circulator.

In an exemplary embodiment of the present invention, the fiber array 218may include one or multiple fibers for detection and illumination. Inanother exemplary embodiment of the present invention, the detection mayoccur using a single fiber. Alternatively, the illumination may occurvia a fiber array, where each fiber is selectively illuminated togenerate multiple focused spots as a function of position on the subjecttissue 250. This exemplary method can provide a scanning of the incidentlight across the sample, while maintaining the probe in a stationaryposition. The fibers may be illuminated and/or detected simultaneouslyor illuminating and/or detecting light from one fiber after another inseries.

The data produced by the detection device 236 may then be digitized byan analog-digital converter 238, and analyzed using imaging proceduresexecuted by the processor 240. The imaging procedures applicable withthe exemplary embodiments of the present invention are described in U.S.Provisional Patent Appn. No. 60/514,769, entitled “Method and Apparatusfor Performing Optical Imaging Using Frequency-Domain Interferometry,”filed Oct. 27, 2003, and International Patent Application No.PCT/US03/02349 filed on Jan. 24, 2003, the disclosures of which areincorporated by reference herein in their entireties. The processor 240is also operatively connected to the pullback device 216, the rotaryjunction 212 and the fluid pump 225.

The diameter of the catheter can be less than 500 μm. Larger diametersmay also be utilized within the scope of the present invention.

Other types of instruments can be used to gather image data. Forexample, the optics of the catheter 200 can be integrated into othertypes of instruments, such as endoscopes or laparoscopes. The optics canalso form a stand-alone unit passed into the accessory port of standardendoscopes or laparoscopes, and/or integrated into another type ofcatheter, such as dual-purpose intravascular ultrasound catheter.

In an exemplary embodiment of the present invention, the detector 236may be a charge coupled device (“CCD”), a photographic plate, an arrayof photodetectors, and/or a single detector. In another exemplaryembodiment of the present invention, the light source 232 can illuminatethe sample with continuous light, continuous broad bandwidth light,wavelength scanning light, or synchronized pulses.

FIG. 3 illustrates an exemplary embodiment of a method/process 300 forgathering data representative of a helical scan if a screening segmentof the subject tissue 250 according to the present invention. Theprocess 300 begins in step 301 where the catheter 200 is inserted andpositioned within the screening segment of the subject tissue 250. Oncethe catheter 200 is inserted and positioned properly, the imaging module232 instructs the fluid pump or operator 225 to inject a bolus oftransparent or semi-transparent fluid into the subject tissue 250, instep 302. Depending on the size of the subject tissue 250, the imagingmodule 232 may alter volume and/or rate of injection of the bolus oftransparent or semi-transparent fluid. In an exemplary embodiment, thesubject tissue 250 is a blood vessel.

In step 304, the imaging module 232 determines whether the imagereceived from the imaging assembly 204 is of a sufficient quality tobegin scanning the subject tissue 250. If the imaging module 232determines that the image is not of sufficient quality, the process 300advances to step 302. Otherwise, the process 300 advances to step 306,where the rotary junction 212 begins rotating the rotateable inner shaft210 and the pullback device 215 begins pulling back the shaft 210.

The imaging module 232 determines whether the image received from theimaging assembly 204 is of sufficient quality to begin scanning byattempting to detect the presence of blood. The imaging module 232 makesthis determination by measuring the amount of scattering the imagingmodality is experiencing and/or by analyzing the spectroscopy registeredby the imaging modality. If the imaging modality is OCT, other methodsmay be used.

When the imaging module 232 measures the amount of scatteringexperienced by the imaging modality, the imaging module 232 determineswhether the light received from the subject tissue 250 is scattered.Saline and other transparent perfusion liquids do not contain anappreciable amount of scattering. Blood on the other hand, is highlyscattering. Due to this effect, a method for determining the presence ofblood may be to observe the intensity of the reflection of light back tothe catheter. Preferentially, certain wavelengths of light may be usedthat have the property that the absorption penetration depth is small inboth water and blood.

When the imaging module 232 is utilizing spectroscopy to determinewhether blood is present, the imaging module 232 can measure thedifferential absorption experienced by the imaging modality. Bloodadjacent to the subject tissue 250 can be detected by utilizingdifferential absorption of blood. In blood which is oxygenated, thereare several absorption peaks in the visible spectrum, e.g., at 520-590nm and 800-900 nm. A simple device may obtain the light scattered backfrom the catheter at these wavelengths, and compare such light to thelight scattered back from an adjacent wavelength where blood absorptionis low. This comparison can be accomplished by a linear combination ofthe intensity of light reflected back by the two wavelengths. Forexample if R(λ₁) is the light reflected back to the catheter on theabsorption peak and R(λ₂) is the light reflected back to the tissue offof the absorption peak, blood can be estimated by severaldifferential/ratiometric combinations of R(λ₁) and R(λ₂):

${D\; 1} = \frac{R\left( \lambda_{1} \right)}{R\left( \lambda_{2} \right)}$${D\; 2} = \frac{R\left( \lambda_{1} \right)}{\left\lbrack {{R\left( \lambda_{1} \right)} + {R\left( \lambda_{2} \right)}} \right\rbrack}$${D\; 3} = \frac{\left\lbrack {{R\left( \lambda_{1} \right)} - {R\left( \lambda_{2} \right)}} \right\rbrack}{\left\lbrack {{R\left( \lambda_{1} \right)} + {R\left( \lambda_{2} \right)}} \right\rbrack}$${D\; 4} = \frac{\left\lbrack {{R\left( \lambda_{1} \right)} - {R\left( \lambda_{2} \right)}} \right\rbrack}{R\left( \lambda_{2} \right)}$

The device for delivery and detection can be a simple side firing singleor multi-mode optical fiber.

If the imaging modality is OCT, another method for detecting blood canbe used. Since OCT is capable of obtaining a cross-sectional image ofthe lumen, it is potentially more sensitive to the presence of smallamounts of blood than is diffuse spectroscopy. The OCT signal from bloodis fairly characteristic, and not commonly observed in other tissues.For example, blood can exhibit a rapid attenuation and a homogeneousappearance. As a result, in one exemplary embodiment, it is possible toprocess the OCT signal to determine if blood is present. A wide varietyof image processing techniques known in the art, such as texturediscrimination, pattern recognition, etc. can be used to identify blood.In one embodiment, in order to determine whether blood is present, twoparameters are determined: (a) the slope of the logarithm of the OCTaxial scan data (attenuation); and (b) the standard deviation of thelogarithm of the OCT axial scan data (signal variance). These twoparameters can differentiate most human tissue types. Other measures ofattenuation and signal variance known in the art can also be utilized todifferentiate blood from arterial wall tissue. Other measurementsincluding probability distribution function statistics, Fourier domainanalysis, high pass filtering, energy and entropy measurements, edgecounting, and N-order moments can be utilized to determine the presenceof blood in the lumen of the blood vessel. OCT can be combined withspectroscopy (e.g., performing OCT at two wavelengths), birefringence,and Doppler to further enhance the capability of OCT for identifyingblood in the lumen. In one exemplary embodiment of the presentinvention, the fluid pump 225 continues injecting the bolus oftransparent or semi-transparent fluid during the step 304.

Turning back to the process 300 of FIG. 3, in step 308, the imagingmodule 232 determines whether the image received from the imagingassembly 204 is of sufficient quality to continue scanning the subjecttissue 250. If the imaging module 232 determines that the image is ofsufficient quality, the process 300 advances to step 306. Otherwise, theprocess 300 advances to step 310. At step 310, the rotary junction 212stops rotating the rotateable inner shaft 210, and the pullback device215 halts the pullback of the shaft 210. If the fluid pump 225 iscontinuing to inject the bolus of transparent or semi-transparent fluid,the fluid pump 225 is instructed to discontinue injecting thetransparent or semi-transparent fluid. If there is catheter motion, thecatheter may be advanced or retracted substantially along thelongitudinal axis of the vessel prior to the next bolus injection inorder to ensure that the subsequent pullback imaging process does notskip over any areas of tissue.

This process represents a feedback control loop where a measure of imagequality is utilized to control the process/conditions under which imagesare obtained. If the image is not of sufficient quality, action is takento improve the image quality before additional images are taken. In anexemplary embodiment, when image quality drops below a predeterminedmeasure but image quality is still sufficient to continue imaging,additional transparent or semi-transparent fluid is injected via thefluid pump 225 improving image quality. In another exemplary embodiment,when image quality drops below a predetermined measure and image qualityis insufficient to continue imaging, imaging is halted. The feedbackcontrol loop may be set up many different ways in order to automate atleast a part of the process 300. A wide variety of image processingtechniques known in the art, such as texture discrimination, patternrecognition, etc. can be used to determine whether or not image qualityof the vessel wall is sufficient to continue imaging.

In an exemplary embodiment, two parameters are determined: (a) the slopeof the logarithm of the OCT axial scan data (attenuation); and (b) thestandard deviation of the logarithm of the OCT axial scan data (signalvariance). These two parameters can differentiate most human tissuetypes. Other measures of attenuation and signal variance known in theart can also be utilized to identify and characterize the quality ofimages obtained from arterial wall tissue. These other measurementsincluding image segmentation and blob quantification, morphologicprocessing, probability distribution function statistics, Fourier domainanalysis, high pass filtering, energy and entropy measurements, edgecounting, N-order moments. OCT can be combined with spectroscopy (e.g.,performing OCT at two wavelengths), birefringence, and Doppler tofurther enhance the capability of OCT for assessing image quality.

In step 312, the imaging module 232 determines whether the entire lengthof the screening segment of the subject tissue 250 has been imaged. Ifadditional portions of the screening segment of the subject tissue 250need to be imaged, the process 300 advances to step 302. Otherwise, theprocess 300 advances to step 314 where the imaging module 232reconstructs the helical or three-dimensional scans of the screeningsegment of the subject tissue 250 based on the information gatheredduring the scan. After the helical scans are reconstructed, the imagingmodule 316 can display the reconstructed data (images) and the process300 exits.

FIG. 6 illustrates an imaging system 600 including the speciallymodified optical catheter 202 disposed within a guide catheter 602. Theoptical catheter 202 is identical to the optical catheter 202 asillustrated in FIG. 2A, except that the fluid delivery channel 223 andthe aperture 221 are not necessarily included in the optical catheter202 as illustrated in FIG. 6. The fluid delivery channel 223 and theaperture 221 are replaced by the fluid delivery channel 606 and theaperture 604, respectively. In order to use the imaging system 600, theguide catheter 602 is inserted into a blood vessel and positionedadjacent to a target area to be imaged.

The optical catheter 202 is inserted into the guide catheter 602 untilthe distal end 220 of the optical catheter 202 protrudes beyond theguide catheter 602 (as shown in FIG. 6). Once the guide catheter 602 ispositioned relative to the guide catheter 602, the optical catheter 202operates in the same manner as discussed above in connection with FIGS.2A, 2B, 3, 4, and 5, with the exception that the fluid pump 225 injectstransparent or semi-transparent fluid into the fluid delivery channel606 and through the aperture 604 to the target area instead of utilizingthe fluid delivery channel 223 and aperture 221.

In an exemplary embodiment, the guide catheter 602 is used as the fluiddelivery channel. The guide catheter 602 does not necessarily include aspecial purpose fluid delivery channel 606. The fluid pump 225 isconnected directly to the guide catheter 602 and transparent orsemi-transparent fluid is provided at the target area via the guidecatheter 602. In another exemplary embodiment, the imaging assembly 204protrudes beyond the distal end of the guide catheter 602. The imagingof the target area takes place while the imaging assembly 204 of theoptical catheter 202 protrudes from the distal end of the guide catheter602. In a further exemplary embodiment, the guide catheter 602 istransparent and the optical catheter 202 is inserted into the guidecatheter 602 until it is adjacent to the target area. The imagingassembly 204 of the optical catheter 202 does not protrude beyond theguide catheter 602 and the imaging of the target area takes place whilethe optical catheter 202 is within the guide catheter 602.

The foregoing merely illustrates the principles of the invention.Various modifications and alterations to the described embodiments willbe apparent to those skilled in the art in view of the teachings herein.It will thus be appreciated that those skilled in the art will be ableto devise numerous techniques which, although not explicitly describedherein, embody the principles of the invention and are thus within thespirit and scope of the invention.

What is claimed is:
 1. An apparatus for imaging a structure, comprising:an article of manufacture; a first fluid delivery arrangement configuredto deliver a volume of a fluid to an external location with respect tothe article of manufacture; and an imaging second arrangement configuredto obtain information associated with the structure at least one ofbefore, during or after the volume of the fluid is delivered to theexternal location, wherein at least one of the second arrangement or thearticle of manufacture is translated along a path which approximatelycorresponds to an axis of extension of a surface, wherein thetranslation is automatically performed at a rate of more than 1mm/second using the information provided from a processing arrangement,wherein the first fluid delivery arrangement delivers the fluid to aproximal end of a guide catheter of an article of manufacture, andwherein the fluid flows through an aperture formed through the guidecatheter.
 2. An apparatus for imaging a structure, comprising: anarticle of manufacture; a first fluid delivery arrangement configured todeliver a volume of a fluid to an external location with respect to thearticle of manufacture; and an imaging second arrangement configured toobtain information associated with the structure at least one of before,during or after the volume of the fluid is delivered to the externallocation, wherein at least one of the second arrangement or the articleof manufacture is translated along a path which approximatelycorresponds to an axis of extension of a surface and rotated around thepath, wherein the translation is performed at a rate of more than 1mm/second automatically using the information, and wherein the rotationis performed at a rate of at least above 30 rotations/secondsubstantially at the time that the information is being obtained by thesecond arrangement.
 3. The apparatus of claim 1, wherein the rotation isperformed at a rate of at least above 50 rotations/second.
 4. Theapparatus of claim 1, wherein the information includes optical coherencetomography information.
 5. The apparatus of claim 1, wherein theinformation includes image information.
 6. The apparatus of claim 1,wherein the fluid is substantially transparent to a radiation utilizedby an imaging modality, which is a time domain optical coherencetomography, a spectral domain optical coherence tomography or an opticalfrequency domain imaging.
 7. The apparatus of claim 1, wherein the guidecatheter is (i) part of the apparatus, and (ii) configured to receivethe article of manufacture therein.
 8. The apparatus of claim 1, whereinthe processing arrangement is configured to control at least one of thefirst fluid delivery arrangement or the second arrangement as a functionof the information.